The invention relates to loudspeakers and more particularly to resonant panel-form loudspeakers, e.g. of the general kind described in U.S. application Ser. No. 08/707,012, filed Sep. 3, 1996, and known as xe2x80x9cdistributed modexe2x80x9d or xe2x80x9cDMxe2x80x9d loudspeakers, installed in vehicles such as automobiles, railway carriages, aeroplanes, omnibuses and the like.
At present vehicle trim is designed and manufactured solely for the purpose of interior fitting, decoration, sound insulation etc. and is also connected to and may form the support for accessories such as arm rests, cup holders, control buttons, grab handles, levers, knobs and the like. As such the usual constraints of moderate cost and relative unimportance of weight have led to a vehicle trim panel type which is often of high mechanical impedance (Zm) and high mass per unit area (u).
It is however known from WO97/09842 to provide a distributed mode loudspeaker which is integral with a vehicle interior trim panel component.
An object of the present invention is to provide a class of resonant panel-form loudspeaker integrated with other panel form structures forming the interior trim in a vehicle, e.g. an automobile, railway carriage, aeroplane, omnibus or the like whereby the integrated structure is configured to fulfil the joint requirements for vehicle trim use and as a loudspeaker.
According to the invention, there is provided a method of making a vehicle interior trim panel having at least one integral resonant bending wave loudspeaker panel, comprising designing the trim panel to comprise at least one panel area capable of and intended to operate as a resonant bending wave loudspeaker, making a prototype trim panel to the design, optimising at least one parameter of the prototype panel as concerns its behaviour as a resonant bending wave loudspeaker by obtaining the standard deviation, as frequency is varied, of the mechanical impedance of the panel as a function of the at least one parameter, selecting a value or values of said at least one parameter that result in a minimum of said standard deviation of the mechanical impedance of the panel, and making a trim panel in which the at least one parameter to be optimised has the selected value or values. The prototype panel may be further analysed by laser scanning and/or by proximate analysis of acoustic output over area.
The at least one panel area of the trim panel may be designed as a distributed mode loudspeaker e.g. as described in application Ser. No. 08/707,012, which is incorporated herein by reference in its entirety.
The at least one panel area of the trim panel may be designed to have an effective frequency distribution of at least the first few, e.g. say six, resonant modes of bending wave behaviour.
The method may comprise designing the at least one panel area so that resonant modes associated with one axis of the said at least one panel area are interleaved in frequency with resonant modes associated with another axis of the said at least one panel area.
The method may comprise designing the at least one panel area to comprise means defining a boundary of the said at least one panel area.
The trim panel may be made by moulding using heat and/or pressure.
From another aspect, the invention is a vehicle interior trim panel made by the method set out above.
It has been shown in DM art, e.g. application Ser. No. 08/707,012, that panels may be configured and designed to have useful regions of modal distribution for desirable sound radiation including specific recommended geometries or implied geometries. In addition panels may have useful DM operable regions developed by analytical methods so that useful acoustic output, which may augment the DM operable region, is obtainable from larger areas of the panel working below the modally dense frequency range and which may include useful contribution of sound from area drive in a substantially whole body diaphragm mode approximating the action of a drum. Through appropriate design and analysis the behaviour in this range may be tailored to provide a wider and more useful frequency range of sound than using DM alone. The larger driven area may thus provide a lower frequency support to the higher frequency and more critical DM region.
The method may comprise designing/specifying trim components of reduced mass and lower mechanical impedance for vehicles, which are properly adapted largely to maintain their original functionality but which additionally have region(s) and/or inbuilt area(s) of panel which are suited to bending wave speaker operation and where the operable sections are configured to have a useful distribution of modal resonances suitable for producing an effective sound output when vibrational energy is input to these areas/sections via a suitable electrodynamic exciter connected to an audio signal means. Moulding techniques involving heat and/or pressure may be employed to make these combination speaker/trim assemblies to provide a strong integrated assembly compatible with standard production techniques.
The trim speaker may have single or multiple exciters disposed for the desired coupling to the useful modal resonances.
The trim speaker may have a sub panel(s) moulded or co-moulded or otherwise integrally fixed into position on the trim panel. This sub panel may be seamless in appearance when viewed from the side accessible to the vehicle user. The sub panel(s) may be full range or optimised for specific ranges, e.g. the higher frequencies. In the latter case the acoustic damping and mechanical impedance may be optimised for improved high frequency modal resonant behaviour. The sub panel(s) may work in conjunction with the main panel and where the main panel may be optimised for the lower frequencies.